During the past years, more and more content users are downloading the desired content into smart phones, tablets, personal computers and even the traditional TV set. Also, the amount of information exchanged between users has dramatically increased. One of the responses of the communication network operators to this increase traffic is to deploy optical fiber instead of the traditional copper wire, which is known to have a larger transmitting capability.
An example of a network that uses optical fiber is a passive optical network (PON). PON is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises. A PON 10 is illustrated in FIG. 1 and includes an optical line terminal (OLT) 12, for example, at the service providers central office and a number of optical network units (ONUs) 14 (also known as optical network terminal (ONT)), for example, near end users. A splitter 16 is provided along the optical fiber 18 to split the signal from the OLT for the ONUs. A PON configuration reduces the amount of fiber and central office equipment required compared with point to point architectures. A passive optical network is a form of fiber-optic access network.
A PON takes advantage of using one wavelength for downstream traffic (from OLT to ONU) and another for upstream traffic (from ONU to OLT) on a single fiber. Because of the fact that OLT can continuously transmit information to the ONUs while the ONUs need specific time allocations for transmitting their data, various mechanisms have been implemented for having the ONUs equipment on and off at certain times to accommodate the upstream traffic. For example, such a mechanism is the multi-point control protocol (MPCP) for which in the point-to-multipoint downstream direction, the OLT is able to broadcast data to all ONUs due to the directional property of the optical splitter/combiner and in the upstream direction, as the ONUs cannot communicate directly with one another, each ONU is able to send data only to the OLT in a multipoint-to-point manner. However, these mechanisms are not energy efficient as discussed next.
Many efforts have been devoted to reduce the energy consumption of wired and wireless access networks. PONs have received attention due to their ability of providing the lowest energy consuming solution for broadband access, apart from offering large capacity, small attenuation, low operational expenditures, and longevity. Various results reported in the field (e.g., Tucker et al., “Evolution of WDM Optical IP Networks: A Cost and Energy Perspective,” IEEE/OSA Journal of Lightwave Technology, vol. 27, no. 3, pp. 243-252, February 2009) show that PONs consume less energy per bit than hybrid fiber-copper based access technologies, e.g., fiber-to-the-node (FTTN), and wireless access solutions, e.g., WiMAX.
Further, it was shown (e.g., Lange and Gladisch, “On Energy Consumption of Telecommunication Networks-A Network Operator's View,” in Proc., OFC/NFOEC, Workshop on Energy Footprint of ICT, San Diego, Calif., USA, March 2009, pp. 1-3) that PONs are also more energy efficient than fiber-to-the-home (FTTH) network technologies such as point-to-point and active optical access networks. This property assures future PON deployments in response to concerns about the green-house impact of the Internet.
With regard to the PON 10 shown in FIG. 1, it is noted that in the point-to-multipoint downstream direction, the OLT is able to broadcast data to all ONUs due to the directional property of the optical splitter/combiner. In the upstream direction, however, ONUs cannot communicate directly with one another. Instead, each ONU is able to send data only to the OLT in a multipoint-to-point manner. To allow all ONUs to share either wavelength without channel collisions, time division multiplexing (TDM) is considered. In both IEEE Ethernet PON (EPON) and ITU-T Gigabit PON (GPON), a polling mechanism is proposed to facilitate bandwidth allocation. More specifically, each ONU reports its required bandwidth (i.e., queue occupancy) to the OLT and the OLT informs the ONUs about their assigned upstream transmission windows in the downstream frame. EPON introduces REPORT and GATE messages in its upstream and downstream directions to report and specify the ONU upstream transmission grants, respectively. In GPON, each upstream and downstream frame contains a dynamic bandwidth report (DBRu) and a physical control block (PCBd). DBRu is used for reporting the required bandwidth by an ONU. PCBd includes a bandwidth map (BWmap) field to specify the ONU upstream transmission grants. Note that various dynamic bandwidth allocation (DBA) algorithms have been proposed in the literature, while no specific DBA algorithm is specified in IEEE EPON and ITU-T GPON standards.
The XG-PON standard introduces the following low-power operation modes: (i) shedding, (ii) sleeping (or known as cyclic sleeping), and (iii) dozing. In ONU power shedding mode, non-essential functions are powered off or reduced. While the transmitter and receiver modules of ONU are powered off in the sleeping mode, the doze mode turns off the transmitter part for substantial periods of time only. The sleeping mode is further subdivided into fast sleep and deep sleep. In the fast sleep mode, the power save state sojourn consists of a sequence of sleep cycles, each composed of a sleep period and an active period. In the deep sleep mode, the transmitter and receiver remain off for the entire duration of the power save state sojourn. The evaluation of the cyclic sleep and doze operation modes show that the cyclic sleep experiences a greater power saving. However, the cyclic sleep results in a reduction of the Quality of Service (QoS) performance for longer sleep intervals. When deploying the doze mode, the power consumption of PON decreases without incurring any QoS penalties.
The IEEE 803.3az energy efficient Ethernet (EEE) standard introduces an overhead for waking up and sleeping the Ethernet link, where the low-power idle mode is defined when there is no packet to transmit. In EEE, packet coalescing, which assembles multiple packets before sending them, can further improve the channel and energy efficiency by reducing the number of wake and sleep time intervals. However, various studies have shown that coalescing increases delay and even causes packet loss in downstream buffers.
Accordingly, it would be desirable to provide devices, systems and methods that are more energy efficient while reducing the negative impact on the QoS.